Cavity induced vibration of flexible hydrofoils |
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| Affiliation: | 1. Department of Mechanical Engineering, Faculty of Engineering, Ferdowsi University of Mashhad, P.O. Box 91775-1111, Mashhad, Iran;2. State Key Laboratory for Strength and Vibration of Mechanical Structures, International Center for Applied Mechanics (ICAM), School of Aerospace Engineering, Xi''an Jiaotong University (XJTU), Xi''an, China;1. Department of Structural Engineering, University of California, San Diego, La Jolla, CA 92093, USA;2. Hobie Cat Company, Oceanside, CA 92056, USA;1. School of Mechanical Engineering, Beijing Institute of Technology, Beijing 100081, China;2. Aviation Engineering School, Air Force Engineering University, Xi’ an, 710051, China;3. College of Water Resources and Civil Engineering, China Agricultural University, Beijing, 100083, China |
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| Abstract: | The objective of this work is to investigate the influence of cavity-induced vibrations on the dynamic response and stability of a NACA66 hydrofoil at 8° angle of attack at Re=750 000 via combined experimental measurements and numerical simulations. The rectangular, cantilevered hydrofoil is assumed to be rigid in the chordwise direction, while the spanwise bending and twisting deformations are represented using a two-degrees-of-freedom structural model. The multiphase flow is modeled with an incompressible, unsteady Reynolds Averaged Navier–Stokes solver with the k–ω Shear Stress Transport (SST) turbulence closure model, while the phase evolutions are modeled with a mass-transport equation based cavitation model. The numerical predictions are compared with experimental measurements across a range of cavitation numbers for a rigid and a flexible hydrofoil with the same undeformed geometries. The results showed that foil flexibility can lead to: (1) focusing – locking – of the frequency content of the vibrations to the nearest sub-harmonics of the foil׳s wetted natural frequencies, and (2) broadening of the frequency content of the vibrations in the unstable cavitation regime, where amplifications are observed in the sub-harmonics of the foil natural frequencies. Cavitation was also observed to cause frequency modulation, as the fluid density, and hence fluid induced (inertial, damping, and disturbing) forces fluctuated with unsteady cavitation. |
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| Keywords: | Cavitation Vibration Lock-in Hydrofoil Flexible Frequency modulation |
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